On the use of impedance detuning for gastrointestinal segment tracking\n of ingestible capsules

Abstract

During their travel through the gastrointestinal tract, ingestible antennas\nencounter detuning in their impedance response due to varying electromagnetic\nproperties of the surrounding tissues. This paper investigates the possibility\nof using this impedance detuning to detect in which segment of the\ngastrointestinal tract - stomach, small intestine, or large intestine - the\ncapsule is located. Meandered dipole antennas operating in the 433 MHz\nIndustrial, Scientific, and Medical Band are designed for this purpose. The\nantennas conform to the inner surface of 3D-printed polylactic-acid capsules\nwith a shell thickness of 0.6 or 0.4 mm. The impedance response is first\noptimized numerically in a homogeneous cylindrical phantom with time-averaged\nelectromagnetic properties. The magnitude and the phase of the reflection\ncoefficient are then obtained in different tissues and compared with\nsimulations and measurements. The experimental demonstration is carried out\nfirst using tissue-mimicking liquids and then in a recently deceased ex vivo\nporcine model. The minimum change in the phase between different\ngastrointestinal tissues was determined to be around 10 degrees in the porcine\nmodel, indicating that the changes in the impedance response, particularly the\nchanges in the phase, provide sufficient information to follow the position of\nthe capsule in the gastrointestinal tract.\n